1. Field of the Invention
The embodiments of the invention generally relate to silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) and, more particularly, to a collector-up SiGe HBT having frequency capabilities in the terahertz (THz) range and a method of forming the HBT structure.
2. Description of the Related Art
Currently, silicon germanium (SiGe) hetero-junction bipolar transistors (HBTs) have frequency capabilities in the gigahertz (GHz) range. However, traditional SiGe HBT structures and methods of forming those structures must be rethought in order to achieve frequency capabilities in the terahertz (THz) range. Specifically, in order to achieve frequency capabilities in the THz range, collector-to-base parasitic capacitance and collector resistance must be substantially lowered. Previously, collector-up SiGe HBT structures were developed in an attempt to achieve such higher frequency capabilities. However, these collector-up SiGe HBT structures were not effective as they were unable to maintain or lower base-to-emitter capacitance, were unable to lower or maintain emitter resistance and/or were unable to maintain or lower base resistance or, more specifically, were unable to lower resistance in the link between intrinsic and extrinsic base regions. Thus, there is a need in the art for a new THz capable SiGe HBT structure and method of forming such a structure. More particularly, there is a need in the art for a new collector-up SiGe HBT structure and method that provides substantially lower collector-to-base parasitic capacitance and collector resistance, while also lowering or maintaining base-to-emitter capacitance, emitter resistance and base resistance in order to achieve frequency capabilities in the THz range.